A heat exchanger of this kind is known in the art, for example, as disclosed in Japanese Patent Publication No. 2005-191527, according to which an inner fin is provided in a fluid pipe, through which heating medium flows, so as to increase a heat transfer area between the heating medium and the fluid pipe, so that heat exchange between the heating medium and a physical object (to be cooled down through heat exchange) is facilitated and thereby heat exchange performance is improved.
According to the heat exchanger of the above prior art (Japanese Patent Publication No. 2005-191527), in a case that a width dimension in the fluid pipe does not coincide with a value, which is calculated by multiplying a fin pitch of the inner fin by an integral number, it is not possible to equally arrange the inner fin in the fluid pipe over its entire width direction. In other words, there remains such a space in the fluid pipe, in which the inner fin does not exist. In such a case, since the heating medium preferentially flows through such a space (in which the inner fin does not exist), the heat exchange performance may be decreased as a result that an amount of the heating medium flowing through a space in which the inner fin is provided in the fluid pipe will be decreased.